Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 105808
Title Energy balance of a sparse coniferous high-latitude forest under winter conditions
Author(s) Gryning, S.E.; Batchvarova, E.; DeBruin, H.A.R.
Source Boundary-Layer Meteorology 99 (2001). - ISSN 0006-8314 - p. 465 - 488.
DOI https://doi.org/10.1023/A:1018939329915
Department(s) Meteorology and Air Quality
PE&RC
Publication type Refereed Article in a scientific journal
Publication year 2001
Abstract Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub-arctic boreal forest with snow covered ground were analysed. The measurements represent late winter conditions characterised by low solar elevation angles. During the experiment (12-24 March 1997) day and night were about equally long. At low solar elevation angles the forest shades most of the snow surface. Therefore an important part of the radiation never reaches the snow surface but is absorbed by the forest. The sensible heat flux above the forest was fairly large, reaching more than 100 W m-2. The measurements of sensible heat flux within and above the forest revealed that the sensible heat flux from the snow surface is negligible and the sensible heat flux above the forest stems from warming of the trees. A simple model for the surface energy balance of a sparse forest is presented. The model treats the diffuse and direct shortwave (solar) radiation separately. It introduces a factor that accounts for the shading of the ground at low solar elevation angles, and a parameter that deals with the partial transparency of the forest. Input to the model are the direct and diffuse incoming shortwave radiation. Measurements of the global radiation (direct plus diffuse incoming shortwave radiation) above the forest revealed a considerable attenuation of the global radiation at low solar elevation. A relation for the atmospheric turbidity as function of the solar elevation angle is suggested. The global radiation was simulated for a three month period. For conditions with a cloud cover of less than 7 oktas good agreement between model predictions and measurements were found. For cloud cover 7 and 8 oktas a considerable spread can be observed. To apply the proposed energy balance model, the global radiation must be separated into its diffuse and direct components. We propose a simple empirical relationship between diffuse shortwave and global radiation as function of cloud cover.
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